ANSI C Based OPC UA Client/Server/PubSub SDK
PubSub SDK Overview

This part of the documentation contains general information about the PubSub functionality in the SDK.


Since the OPC UA PubSub Messaging Concept is just another option to send data and event notifications instead of using the OPC UA Client/Server Subscription Concept, there is no additional application specific code necessary to support PubSub.

An existing OPC UA server implementation can activate the PubSub support by linking the additional PubSub Stack and SDK integration. This functionality is available as additional option and can be activated or deactivated through compiler and project settings. The PubSub support is only included in the 'OPC UA Client Server PubSub SDK Bundle'.

The default integration of PubSub into an OPC UA server can be configured to send variable values in PubSub messages. These variables must exist in the Publisher address space. It can also be configured to receive PubSub messages as Subscriber and to write values from the received messages to existing variables in the Subscriber address space.

The PubSub configuration is stored in a binary file following the standard OPC UA PubSub file format. The configuration can either be provided as file by the OPC UA server application or can be downloaded/modified through the OPC UA server interface. The Getting Started with PubSub Configuration describes how a configuration can be created.

The PubSub communication model is described in OPC UA PubSub Messaging Concept. This chapter provides an overview for the different components of a PubSub communication environment and an introduction for the PubSub configuration model.

As described in PubSub Stack and SDK integration, the PubSub stack allows the integration of custom processing of messages by registering callbacks. This is especially necessary for real-time applications that need to optimize message processing and need to control timing. The corresponding hooks are described in Custom PubSub Message Handling.

See OPC Unified Architecture Overview for an introduction to the different building blocks of the OPC Unified Architecture including the PubSub communication model with Messaging Model for PubSub and PubSub Protocol Binding.

See also OPC UA Client/Server vs. PubSub for more details regarding use cases for client/server or PubSub.

The following pages provide further information on the PubSub functionality in the SDK: